Robert abbott hadfield



R. A. HADFIELD AND A. G. M. JACK.

CAP FOR ARMOR PIERCING PROJECTILES" RPPHCATION FILED MAY 26; 1914.

Patented July 15. 1919.

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ROBERT ABBOTT HAIDFIEL D, OF WESTMINSTER, LONDON, AND ALEXANDER GEORGE MACKENZIE JACK, OF SHEFFIELD, ENGLAND.

CAP FOR ARMOR-PIERCING PROJECTILES.

Specification of Letters Patent.

Patented uly 15, 1919.

To all whom it mag concern Be it known that we, Sir Bonner Anno'r'r HADFIELD kni ht. F. R. 8.. and ALEXANDER GEORGE MACKEXZIE JACK, subjects of the King of Great Britain and Ireland, residing, respectively, at Yl estminster, in the county of London, England, and Sheiiield, Yorkshire, England, have invented Improvements in orRelating to Caps for Armor-Piercing Projectiles, of which the following is a specification.

This invention relates to caps for armor piercing projectiles and consists inthe discovery that a great in'iprovement in the penetration of armor plate may be effected by hardening the cap to a limited degree in distinction .to the very high degree heretofore described and practised and that the improved result may be accomplishedby a cap of comparatively small size.

The function of the. cap is primarily to support the point of the shot-itself sothat it will not be broken down at the instant of impact, and also, if possible, to effect initial penetration, or weakening, of the plate, and thereby prepare the way for the shot itself and make penetration easier.

Heretofore the hardening of caps has been suggested and such caps have been practically used to some ekt'ent' but a very high degree of hardening was aimed at, approaching or equaling the hardness of the armorplate itself- So far as we know it has never.

occurred to anyone that this high degree of hardness was not the most desirable, much less that a better effect could be obtained by lowering the hardness. This high degree (some-times described as glass scratching" hardness) was about or above 610 on the Brinell ball scale, possibly much higher.

After years of study and experiment and many tests, We however, have found that the aforesaid high degree of hardness applied to caps tends to produce brittleness, so that dened to a degree substantially below that high degree above referred to will notonlvi reinforce the point of the shot itself but will initially perforate the plate or at least start, i

the fracture thereof.

A degree of hardness not above about 560 is substantially below said glass-scratching or dead hardness and gives greatly improved results, but we recommend a hardness of about 515 to about 525. This degree of hardness should be aimed at as being about the best but the improved results may be obtained byan approximation thereof, even as low as about T60 to 4'0 and therefore we specify the last named degre as about-the lowest that will bring the cap within the limits of our invention. p

This limited hardeningprescribed by us is so substantially.below the high degree heretofore aimed at'and gives such characteristically new and improved results. that we prefer to refer to our caps and to their.

peculiar degree of hardness as "stifi'enmF and stiffness to distinguish from hardened and hardness for this seems to us a better descriptive term and better to indicate the difference from the old c'aps.

lVe have also discovered that it is better to reduce the extent of the stitfness" or the amount of the stiffened material: we prefer that it should not amount to over about five (5) to about ten' (10) per cent. of the. whole cap; in some cases not over about three (3) to four (l) per cent, whcrebywc have been able greatly to reduce the size of the caps and to attain'successful results with smallcaps. And diminution in the size of the cap is important, for, to preservethe ballistics, the total weight of the projectiles must not vary, and the weight of the cap is just so much taken from the weight of the shot itself, and by so much is reduced the capacity of the shot 'to perforate. as well a the size of the powder chamber, the strength of the wall. etc. Therefore even a slight diminution in the size of the ('apbccolncs important for the weight subtracted from the cap may be added to the weight of the shot itself.

f In other words the important feature of our inventlon IS the d1scover 'v that a cap having a stiffened tip will set back the plateor start the perforation thereof better than an ordinary unhardened cap, butthat the degree of hardness must be limited, for if carried too far, that is to or approaching a hardness of about 610, the purpose of the hardening is largely defeated, for the cap is lacking in the requisite quality of resistance perforation of the plate and thereby causethe same shot much more effectively to perforate the plate, whether fired normally or obliquely, than has ever before been accomplished. Furthermore, the cap so hardened may be greatly reduced in'size without reducing its effectiveness and a more or less gradual diminution from the stiffened front portion rearwardly toward the point of the shot is advised.

The better to explain our invention, reference is made to the drawings herewith. Figure 1 thereof shows in longitudinal section a cap of desirable shape and a portion of the shot to which the capis applied. Fig. 2' is a similar section, much reduced in scale. showing. the entire shot to illustrate the small size of the cap. The shape of the cap here shown is desirable but we do not limit ourselves to that. shape for our invention can be applied with excellent results to caps of various shapes, conical, pointed, rounded or ofother desired shape. Fig.

I 3 is a View similar to Fig. 1 showing a modiwith this stiffened portion not over about fication. I

In Fig. 1 we have indicated the degree and extent of the hardening and the gradual diminution thereof.rearwardly toward the point of the shot. While it is of course not possible to harden-the cap with absolute accuracy as to degree and extent, yet the results here indicated are approximately correct. A indicates the hardened or stiffened front portion of the cap; this is the cross hatched portion varying somewhat in extent. Good results have been attained of the entire cap. The hardness of this portion will vary somewhat and it can not be of absolutely uniform hardness but as aforesaid we should place the limit at not aboveabout 560. Projectiles have attained excellent results, as hereinafter described, with this portion stiffened from about 475 to 515. y

In zone B, whose extent is roughly indicated by the lines C to D, the hardness will be less, that is desirably from about 490 to about450, In zone E, approximately outlined by the lines D and F, the hardness will gradually diminish from 450, the bulk of this zone being from about 400 to about 350. The hardness of the bulk of the remainder behind about the line F will be much lower, varying from 250 to 220 down to about'190 more or less.

While the essential feature of the .invention is the stiffening of'the front portion of the cap as aforesaid, we recommend in addition a gradually diminishing hardness from said front stiffened portion rearwardly toward the point of the shot, substantially as described, so that the portion of the cap adjacent said point shall be soft and tough, or comparatively soft. From this it results that upon impact of the capped projectile with the plate the'hard point of,tl1e shot will pass through cap material of gradually increasing stiffness, or

hardness, and will reach and perforate the plate without being suddenly subjected to contact with the extremelyhard surface of the armor plate. As a result the point of the projectile is supported, until it enters the plate, with a graduallyincreasing pres sure from the'moment of impact of the cap tip with the hard surface of the plate, and the sudden shock to which the point of the projectile is usually subjected in passing through the relatively soft metal of the cap and striking the hard metal of the plate, is

avoided, greatly reducing the danger of fracturing the point of the shot.

The cap may be stiffened by any suitable L method, 'for instance by heating up to a temperature of about 850 C. and then quenching in water or other suitable medium for a sufiicient time; .Or even may be overhardened and then tempered to reduce the hardness to the desired degree, though we do not recommend this latter method.

We do not propose to limit ourselves to any particular composition of metal for the cap, for any well known material may be used, for instance a steel containing a suflioient amount of carbon, nickel and chromium to permit the end or tip of the cap to be, stiffened leaving the bulk of the remainder of the cap tough and relatively soft. lVe do not mean by this to imply that the toughness of the front portion is reduced for on the contrary one of the great advantages attained by our invention is that said' front portion is maintained at-a high degree of toughness. Excellent results have been attained in tests with projectiles providedavith our new cap. In certain recent tests several 14 projectiles fitted with our 'K. C. 13-} inch plate inclined at ten degrees.

Other tests have since been made with shot of comparatively an old type; these tests were made obliquely. Some of the shot were fitted with the ordinary cap; some with the cap described in this application in weight only 311 70 to 4% of the total weight of the v projectile. The shot fitted with the new cap went through unbroken; those with the old \also of smallsize.

In the process of stiffening our caps, it is possible that in some cases a trifling thickness of the metal at the point might be found to be hardened abovethe. degree "specified by us, but such would be a superficial hardening ofonly the skin portion of the cap and would not be a substantial modification of the stiffened condition prescribed by us, nor a departure from our invention. f

What we claim is '1. A cap for an armor piercing projectile having its front portion stiffened to from about 460 to about 560 ball hardness and gradually diminishing in stiffness rearwardly from said front portion.

2. For an armor piercing projectile, a cap having a stiffened tip the Weight of which is of the order offrom three to ten per cent. of the weight of the whole cap and the hardness of which corresponds substantially to a ball hardness of from about 4.60 to 560.

3. An armor piercing projectile comprising a projectile proper and a cap having a stiffened and toughened tip or forward end, the final stiffness corresponding to a ball hardness of, the order of from about 460 to 560 and the weight of such stiffened portion being of the orde-rjof from about three to ten per cent. of the weight of the cap.

4. For an armor piercing projectile, a cap having a stiffened tip, the stiffness thereof corresponding to a ball hardness of not over about 560 and substantially below glass scratching hardness, and the portion of the cap adjacent the tip being of gradually diminishing hardness, the narrow zone at the front end being from about 560 to 475 ball hardness, the next zone being of about 490 to about 450. the bulk of the next zone being from about 400 to about 350, and the remaindcr of the cap being from about 250 to 190. said zones being. approximately of equal width, and the three zones occupying not more than one-half the bulk of the cap from the extreme tip to the portion to lie in contact with the tip of the projectile.

For an armor piercing projectile a cap having its tip' hardened or stiffened to a high degree. but not above about 560 ball hardness.

6. For an armor piercing projectile, a cap having its tip stiffened to about 515 to 525 ball hardness. 7. For an armor piercing projectile, a cap having its tip stiffened to a high degree, but not above about 560 ball hardness, and gradually diminishing in stiffness rearwardlyfrom said tip.

8. For an armor piercing projectile, a cap from about 460 to 560 ball hardness, the remainder of the cap being very tough but comparatively soft.

9. For an armor piercing projectile, a cap having its tip stiffened to from about 460 to about 560 ball hardness and being in weight from about 3%;% to about 7:}% of the entire projectile.

10. A cap for an armor piercing projectile, the portion of which that will be forward .of the point of the projectile to which the cap is to be fitted, is of gradually increasing stiffness in a forward direction, the final degree of stiffness adjacent to the point or tip of the cap corresponding to a ball hardness of the order of about 560.

11. A cap for an armor piercing projectile, the portion of which that will be forward of the point of the projectile to which .the cap is to be fitted, is of gradually increasing stiffness in a forward direction, the final degree of stiffness adjacent to the point or having its tip very tough and stiffened to tip of the cap corresponding to a ball hardness of the order of about 560, the stiffened port-ion of the cap, corresponding to a ball hardness .of 450 to 560, not constituting more than about three and one half per cent. of the entire cap.

12. A cap for an armor piercing projectile,

having its front portion stiffened to from 450 to 560 ball hardness and gradually diminishing in stiffness rearwardly from said front portion, said stiffened cap weighing about three and one half per cent. to about seven and one half per cent. of the weight of the projectile.

13. A cap for armor piercing projectile, made of nickel chromium steel and having its front portion stiffened to from about 460 to 560 ball hardness and gradually diminishing in stiffness rearwardly from said front portion.

Signed at 22 Carlton House Terrace, lVestminster, England, this thirteenth day of May, 1914.

i tnesses LEONARD ROWLAND,

E. S. HEAP. 

